1. Field of the Invention
The present disclosure relates to electron beam (e-beam) apparatus and methods of operating same. More particularly, the present disclosure pertains to e-beam apparatus for automated measurement systems and automated inspection/review systems.
2. Description of the Background Art
Substrates, such as low-k dielectric and similar wafers, frequently have embedded charges. These embedded charges may cause beam aberration issues in electron beam imaging of such substrates. Such beam aberration issues may include, for example, astigmatism and/or defocusing.
Correcting for such beam aberrations is often a time consuming procedure for automated measurement systems and automated inspection/review systems. Conventional techniques to correct for beam aberrations typically involve adjustments to the strengths of octupole and/or quadrupole electron lenses in the e-beam column hardware. Such conventional beam aberration correction is a relatively slow process and requires additional beam dosage to the substrate which may result in damage to the specimen.
Furthermore, the conventional techniques for beam aberration correction may be limited by the adjustability of the octupole/quadrupole lenses and by other limitations of the e-beam column. Hence, only small amounts of beam aberration are usually correctable with the conventional techniques. In the event of extreme aberrations, the ranges of the adjustable column components typically reach a maximum (“max out”), leading to a failure to correct the high level of aberration.
The present disclosure describes a novel and inventive technique to reduce or eliminate the need for conventional beam aberration correction in certain applications.